1. Field of the Invention
This invention relates to an igniter plug structure improved to present diameter-reduced structure particularly in use for a gas or jet turbine engine of aircraft for example.
2. Description of the Prior Art
The igniter plug particularly used for the gas turbine, has been exposed to a jet stream of ignited fuel. The jet stream causes to wear the plug for a relatively short period of time.
In order to avoid the fast wear of the plug, several suggestions have been introduced as seen in U.S. Pat. No. 3,330,985 patented July 11, 1967 and Japanese Pat. No. 23632/61 published June 6, 1986 for example.
In the U.S. Patent, the plug has an outer shell having an annular ground electrode connected to a lower end thereof. A tubular insulator is placed into the shell to have an annular passageway between the insulator and both the shell and the ground electrode.
In addition a center electrode is placed into the insulator to have the annular passageway therebetween.
A air flow is admitted into both the passageways through openings each provided at the shell and the ground electrode. The air flow through the passageways allows to cool the center an ground electrodes so as to prevent the plug itself from being excessively heated.
In the Japanese Patent, the two passageways of U.S. Patent are communicated to eliminate the necessity of one of the passageways.
This being conductive to shortening a longitudinal dimension of the plug.
The references of both the patents however focus the subject on cooling a firing tip of the center electrode and have no suggestion about employing a spark-erosion resistant tungsten metal for the ground electrode.
If the tungsten metal is applied to the igniter of the above patents, it would be difficult to provide an opening with a diameter-reduced ground electrode due to the poor machinability of the tungsten metal.
Further the tungsten metal would be fast oxidized to deteriorate when the gas flow is unable to drop the temperature of the ground electrode below 650 degrees centigrade.
Therefore, it is a primary object of this invention to provide an igniter plug structure which is capable of directly cooling the ground electrode with simple construction, thus enabling to applying the tungsten metal to the ground electrode without let and hindrance, and further readily responding to a diameter-reduced igniter plug particularly in use for a gas turbine engine.
Accordingly, there is provided the igniter plug comprising; the outer annular metallic shell having the annular ground electrode connected to the lower end thereof; the tubular insulator concentrically placed into the metallic shell and having a centerbore therethrough; the center electrode longitudinally positioned within the centerbore and having the firing tip which forms a spark gap region with the lower end of the ground electrode; a plurality of grooves provided with an outer surface of the ground electrode, one open end of each groove being terminated at the lower end of the ground electrode so that the grooves admit the air flow to pass along the grooves to cool the plug including the ground electrode at least.
With the igniter plug mounted on the gas turbine engine, the air flow through a secondary air passage is admitted into grooves to pass therealong so as to enter a combustion chamber. The air flow through the grooves allows to cool the ground electrode as well as the center electrode, thus preventing a temperature of the plug from excessively rising. This makes it possible to apply a spark-corrosion resistant tungsten metal to the ground electrode without let and hindrance. The grooves on the ground electrode readily leads to a tolerable machining so as to present the diameter-reduced igniter plug.
Other objects and advantages of this invention will be apparent from the following description, reference being made to the accompanying drawings wherein preferred embodiments of this invention are shown.